This invention relates to accurate determination of location of a vehicle on a roadway or a waterway relative to a lane boundary.
Satellite-based signal sources, such as the Global Positioning System (GPS) or Global Orbiting Navigational Satellite System (GLONASS) or Low Earth Orbit (LEO), for location determination (LD) can now provide corrected signals with relatively small associated inaccuracy. Previously, a vehicle navigation system might provide a map of a local region, including major roads, and provide an approximate graphical indication of the present location of a vehicle relative to the road system shown on the map. However, it is also of interest to provide a more detailed image showing the vehicle relative to a particular roadway or waterway on which the vehicle is presently located. Here, the associated inaccuracy should be no more than 50 cm, in order that the vehicle be accurately located relative to a particular lane in which the vehicle travels. It would not be sufficient here to merely estimate the vehicle and to provide a snap-to-grid operation that places the vehicle in the roadway or waterway lane that is nearest to the vehicle present location. This is especially true if the LD system is to provide automatic guidance within a roadway lane. If the vehicle xe2x80x9cwandersxe2x80x9d too far afield, the vehicle may collide with a vehicle in an adjacent lane that is moving in the same direction or in an opposite direction.
Another problem that arises here is communication to the vehicle of location correction information and related data that allows an on-board signal processor to determine the vehicle location with sufficient accuracy. Many vehicle communication systems available today only allow transmission of a few hundred bits of relevant information per second. This rather low rate of (correction) information transmission would not permit LD computations and corrections to be made at a rate (one or more times per second or more for each of three or more LD signals received) that is required for automated roadway or waterway guidance. A real time kinematic (RTK) system allows correction of LD signals, such as GPS signals, using LD correction signal sources that are spaced apart from the user by a distance that is usually no more than about 40 km, which strongly limits the region over which a vehicle can operate with one or a few RTK reference stations.
What is needed is a wide area LD correction system that estimates and provides corrected vehicle location up to several times per second, with an inaccuracy of no more than 10-50 cm within a selected roadway or waterway lane, and that indicates when the vehicle is too close to, and moving toward, a lane boundary. Preferably, the system should operate over a wide area, such as a region with diameter between 50 km and 5000 km. Preferably, the system should also determine a velocity at which the vehicle moves toward a nearest lane boundary. Preferably, the system should also allow accurate mapping of lane boundaries for a roadway or waterway.
These needs are met by the invention, which provides a Wide Area location information transmission and processing system that permits communication of location correction data for each of several LD signal sources and that permits computation of corrected location coordinates of a vehicle and graphical, alphanumeric or other display of vehicle location relative to a chosen roadway lane, with an associated inaccuracy of at most 10-50 cm and at a rate of several times per second. An LD correction system, such as DGPS or WAAS for the GPS, determines local corrections for pseudoranges or related measurements for visible LD signal sources (satellites) and uses a wireless transmission system, such as SDARS or FM subcarrier or Sky Station or Private Radio, with modest information transfer rate to deliver the LD correction information to an LD signal antenna and LD receiver carried on a subscriber vehicle. The vehicle LD receiver receives LD signals, corrects the LD signals using the LD correction information, computes the present location and (optionally) velocity of the vehicle relative to a selected roadway or waterway lane on which the vehicle travels. Optionally, the LD receiver provides an alarm signal if the vehicle is approaching a lane boundary too quickly or is too close to a lane boundary. A Wide Area LD correction system can also be used to map boundaries for vehicle travel lanes to provide a database of boundary lane descriptions that can be subsequently used for Wide Area vehicle tracking within a travel lane.
As used herein a xe2x80x9cWide Areaxe2x80x9d LD correction system is an LD correction system with at least three sources of LD correction signals that are spaced at least a selected distance dl apart, where a distance d2 between any location and each of at least two of these LD correction signal sources is greater than about 0.5 d1. The distance dl may be chosen to be a suitably large value, such as 50 km, 100 km, 500 km or 1000 km.